Process for removing carbonic oxide from combustible gases



Jan. 21, 1941. BRANDT 2,229,166

raocnss FOR REMOVING CARBONIC OXIDE FROM COMBUSTIBLE GASES Filed April14, 1938 COPPER CONTACT CONTACT FURNACE IRON CHROMIUM CONTACT IRONCHROMIUM CONTACT GAS SUPPLY INVENTOR Rickard Brandi:

ATTORNEY Patented Jan. 21, 1941 t PROCESS FOR REMOVING C'ARBONIC OXIDE.FROM COMBUSTIBLE GASES Richard Brandt, Berlin, Germany Application April14, 1938, Serial No. 202,130 In Germany November 19, 1935 4 Claims. (01.23-3) The removal of carbonic oxide from gases oboxygen can be veryadvantageously utilised to tained from the distillation of coal or fromgas effect the preheating of the fresh gas for the mixtures containinggas obtained from the dissteam catalysis. Consequently, in individualtillation of coal can, as is known, be effected by cases there may beincorporated in the gas a 5 purifying the initial gas in the usualmanner, somewhat larger quantity of oxygen than is usual and then, afteraddition of steam, subjecting it in the removal of the sulphurettedhydrogen. to so-called steam catalysis,-for example, in the This has theadvantage that the dry purificapresence of an iron chromium contact.Assocition is conducted more economically, because the ated with thestated usual purification there is usual effective quantities per unitof volume of also the removal of sulphuretted hydrogen. As the purifyingmass can be considerably increased. 10

a rule, however, organic sulphur compounds re- It is true that there isalready known a twomain in the gas mixture and pass over the constagecatalysis for the removal of carbonic oxide tact with the gas. from gasmixtures, in which known method,

In the known method of removing carbonic however, in a first stage thereis effected hyoxide, difficulties have been experienced, becausedro'genation of carbonic oxide to form methane 15 for the activity andduration of the contact, the and in a second stage there is effectedconverpresence of oxygen in the initial gas is of subsion of residualcarbonic oxide to carbonic acid stantial consequence. The purificationof the and hydrogen with the aid of the steam or wacoal gas fromsulphuretted hydrogen is, as is ter vapor obtained in the first stage.For this known, eifected with iron purifying masses with methanecatalysis, however, notoriously crude 20 the addition of air. As thesimultaneous regengas or coal gas purified in the usual mannercaneration of the masses cannot be practically efnot be used, while,asregardsits catalytic acfected with a theoretical proportion ofsulphurettion for forming methane, the methane contact ted hydrogen tooxygen, after removal of the is poisoned by slight quantities ofsulphur. Consulphuretted hydrogen the gas always contains a sequently,in the said known method the initial 25 certain quantity of oxygen, as arule about 0.2%. gas must be subjected to further thorough purifi- Theinvention is based on the observation that cation, especially fromorganically bound sulsuch a content of oxygen is the cause of the phur.In contrast therewith, it is an essential rapid wastage of the ironchromium contact in advantage of the method according to theinvenconsequence of the formation of resin-like prodtion that an initialgas containing organic sul- 30 ucts. The invention contemplates,therefore, the phur compounds can be subjected to steam catalremoval ofthe oxygen contained in the gas which ysis. has been freed fromsuiphuretted hydrogen in Such combustion of the oxygen at the pretheusual manner. This is suitably effected by liminary contact has on theone hand the effect leading the gas mixture containing carbonic oxthatthe main contact is no longer damaged 35 ide, in which organic sulphurcompounds may by the formation of noxious products and, constill becontained, before the conversion of the sequently, has a longer life,while, on the other carbonic oxide by steam catalysis, over a prehand,an increase of temperature is obtained.

liminary contact of different composition from If, for example, bypreheating with the conthe main contact, which preliminary contactverted gas in a heat exchanger the fresh gas is 0 has such propertiesthat the oxygen in the gas brought to 0.. then by h p el mi aryommixture is consumed. As the preliminary conbustion, for example, atemperature of 350 C., tact body there is preferably employed copper,can be obtained. but also other metals known for the removal of In orderto be able to effect the temperature oxygen from gas mixtures, forexample, from exchange with suificient temperature drop, the 45electrolytic hydrogen or for analytic determinatemperature differenceobtained by the exothertion in gas analysis, such as platinum,palladimic conversion of carbonic oxide with water to um, nickel, ormetal oxide, come into consideraform carbonic acid is further increasedby the tion. combustion of oxygen in the gas. To obtain a The methodaccording to the invention can temperature drop between the convertedgas and 50 also be advantageously supplemented by prea fresh gas of toC., with the use of coal heating the fresh gas purified in the usualmangas containing 6 to 7% of carbonic oxide, in view .ner before thesteam catalysis or conversion of of the unavoidable heat radiation, forexample, the CO. It has been found that the generation the additionalcombustion of 0.2 to 0.6 volume 55 of heat connected with the combustionof the per cent of oxygen is necessary. The oxygen 5;,

content is thus regulated in correspondence with the desired preheating.It is nolonger, as in the known method, an injurious but a desiredconstituent for the control of the economy.

In a preferred embodiment the additional preheating is effected betweenthe saturation of the gas with steam and the treatment at the maincontact, in this case the steam passes with the gas through the heatexchanger and is thus preheated.

The preheating of the fresh gas with the contact in a heat exchanger isnot necessary in all cases. For example, there are frequently availableat the gas works hot gases of a temperature of 400 to 500 C., which canbe used for heating. In such a caseit is not necessary to introduce tothe fresh gas a supplemental excess of oxygen, but there is obtained inconsequence of the heating with the hot gases the same temperaturerelations if at the preliminary contact there is consumed only thequantity of oxygen which in itself is necessitated by the drypurification.

The converted gas is suitably subjected to a further preparatorytreatment before it is led to the distribution main. For example, theremay be effected more or less complete removal of sulphuretted hydrogen,of benzol, hydrocarbons, carbonic acid, moisture and other constituentssuch as ethylene, for which assistant materials and methods of operationare already known per se.

The copper-containing preliminary contact may be obtained, for example,by saturating pumice with copper nitrate, evaporating the nitrogenoxides and reduction of the copper oxide.

A flow diagram illustrating, more particularly, the following exemplaryembodiment of the invention, is shown on the accompanying sheet ofdrawings.

Example Coal gas containing benzol with 6.5% CO and of otherwise usualcomposition is freed from HzS in known manner with iron purifying massesby passing the same, as it comes through conduit, from the source ofsupply through a. purifier P, air or oxygen being added for example atla in such excess that there results a gas with 0.4 vol. oxygen. Asshown on the said flow diagram, this gas is supplied through conduit Ito a saturator 2 where it is saturated with 350 g. H2O per cubic meter,for example by spraying with hot water, entering the saturator at 3 and,if necessary, by direct contact with steam supplied through conduit 4.The gas, leaving the saturator 2 through conduit 5, is heated to about300 C. in a heat exchanger 6. The resultant preheated gas-steam mixtureflows from the heat exchanger 6 through conduit 1 to the top of contactfurnace 8 and downwardly through the three sub-divisions 9, l and II ofthe latter. The first chamber 9 preferably contains a copper contact,while the second and third chambers contain a different contact,preferably an iron chromium contact. The gas-steam mixture preheated to300, flows first through the contact in chamber 9 whereby it is heatedto about 360 C. as a result of the oxygen combustion which is stimulatedby the copper contact. The gas-steam mixture then flows into chambers l0and II wherein the steam reaction takes place and whereby thetemperature of the reaction mixture is raised to about 400 C. Byaddition of steam or water of condensation through conduit l2 beforeentry of the mixture into chamber II, the temperature of the reactionmixture can be moderated to 375 C. in order that the water-gasequilibrium may be adjusted in this chamber at this temperature. Thereaction mixture leaves the contact furnace 8 at its lower end atapproximately this same temperature and with a CO content of 0.5 to 0.8vol. flows through conduit l3 into the heat exchanger 6 where thesteam-saturated coal gas is heated to about 300. The converted gasmixture flows from heat exchanger 6 through conduit I4 into cooler 15wherein it is cooled by means of water supplied through conduit I6,finally leaving the cooler at I! for further suitable treatment.

Iclaim:

l. A process for the removal of CO from gases comprising coaldistillation products, which comprises passing the gases over a solidabsorbent for impurities of the character of hydrogen sulphide and thelike together with sufiicient oxygen to revivify the said absorbent insitu and to leave a residual oxygen content of about 0.4% in the gases,incorporating steam into the said gases, preheating the resultantmixture to a temperature of about 300 C., passing the preheated mixtureover a copper-containing contact at about 300 C. whereby catalyticcombustion of the oxygen is effected and the temperature of the mixtureis raised to about 360 0., adding steam to the resultant oxygen-freegases, and passing the resultant mixture over an iron-chr0- mium contactat a temperature which will result in steam-catalysis and conversion ofCO.

2. A process as defined in claim 1, the first step of adding steam beingeffected prior to the preheating to a temperature of about 300 C.

3. A process as defined in claim 1, the first step of adding steam beingeffected after the preheating to about 300 C.

4. A process as defined in claim 1, the first step RICHARD BRANDT.

